An ideal OPAMP is used to realize a difference amplifier circuit given below having a gain of 10. If x = 0.025, the CMRR of the circuit in dB is _______.

In the range: 40 - 41

Put x = 0.025



V₂ – V₁ = V${}_d$

$\frac{V_2+V_1}{2}=V_c$

2V${}_c$ = V₂ + V₁

2V₂ = V${}_d$ + 2V${}_c$

$V_2=V_c+\frac{V_d}{2}$

$V_1=V_c-\frac{V_d}{2}$

By using superposition

$V_0=\frac{97.5}{\left(97.5+10.25\right)}.V_2\left(1+\frac{102.5}{9.75}\right)-\frac{102.5}{9.75}\times V_1$

V₀ = 10.41 V₂ – 10.51 V₁

$V_0=10.41\left(V+\frac{V_d}{2}\right)-10.51\left(V-\frac{V_d}{2}\right)$

V₀ = 0.10 V${}_c$ – 10.46 V${}_d$

V₀ = A${}_d$ V${}_d$ + A${}_c$ V${}_c$

$CMRR=\left|\frac{A_d}{A_c}\right|=104.31$

CMRR = 20 log (104.31) = 40.39